Right.....
For a PC grow box you will basically be using light bulbs (CFL`s), these come in either a screw cap or bayonet fitting.
The E27 fittings you were talking about are screw cap fittings, the same light but with bayonet fittings are B27 (E27 and B27 are just codes for describing the size and type of fitting E= screw cap B=Bayonet fitting)
So E27= Screw cap 27mm
B27= Bayonet cap 27mm
Screw cap fittings are mainly for US/Europe use but are getting more popular in the UK
Bayonet fittings are the main type used in the UK and have been for years
So find the BULBS that you want to use (wattage/screw size etc), see if they have a screw cap or bayonet fitting and then buy the relevant sockets for them
Wilkinsons sell all the bulbs/sockets/wire etc yo will need if you want to buy OFFLINE
There are numerous sites including ebay/amazon etc if you want to buy them ONLINE
Before i type more do you know what wattage bulbs you are going to be using or do you need help with that as well?
How many bulbs are you planning on using for your PC grow?
If you let me know this info I will provide you with a shopping list and where to get them and then a wiring diagram for you to wire them up (its very easy to do so dont sweat it)